In general, conventional rain attenuation compensation methods mainly use either power control techniques or diversity techniques. In recent times, new techniques have been developed to compensate rain attenuation by using an adaptive transmission technique.
The rain attenuation compensation methods using the power control techniques are disclosed in U.S. Pat. Nos. 4,261,054 and 4,731,866, which amplify signal powers by a degree of signal attenuation if signal attenuation occurs due to rain. But, the prior arts should include a high power amplifier for supplementing the power margin at the time when the system is designed, and thus causes economical inefficiency.
Another rain attenuation compensation method using the diversity techniques requires to install additional earth station, additional frequency band or satellite according to the kinds of diversity, and therefore causes even serious economical problems.
Rain attenuation compensation methods using adaptive transmission techniques are disclosed in U.S. Pat. Nos. 4,309,764, 4,301,533, 4,837,786, and 4,047,151, that describe a method for allocating a spare time slot to either a user or earth station experiencing excessive attenuation in TDMA (Time Division Multiple Access) technique, a method for reducing data transmission rate in case of excessive attenuation, or a method for enhancing error correction capability by providing spare redundancies in a coding method. These methods mainly use a very basic and simple method for compensating rain attenuation, so that the compensation range is limited and efficiency of rain attenuation compensation is also limited. In addition, these methods do not provide a detailed method for allocating a proper transmission method by estimating rain attenuation and then predicting attenuation at the next sampling time.